Chemical-mechanical planarization ("CMP") processes remove material from the surface of a semiconductor wafer in the production of integrated circuits. FIG. 1 schematically illustrates a CMP machine 10 with a wafer loading/unloading assembly 14, a platen 20, a wafer carrier assembly 30, a polishing pad 40, and a planarizing liquid 44 on the polishing pad 40. The polishing pad 40 may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation fixed abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid 44 may be a conventional CMP slurry with abrasive particles and chemicals that remove material from the wafer, or the planarizing liquid 44 may be a planarizing solution without abrasive particles. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed abrasive polishing pads.
The CMP machine 10 also has an underpad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the polishing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow A) or the drive assembly 26 reciprocates the platen back and forth (indicated by arrow B). Since the polishing pad 40 is attached to the underpad 25, the polishing pad 40 moves with the platen 20.
The wafer carrier assembly 30 has a chuck 31 with a lower surface 32 to which the backside 15 of a wafer 12 may be attached. The wafer 12 may alternatively be attached to a resilient pad 34 positioned between the wafer 12 and the lower surface 32 of the chuck 31. The chuck 31 may be a weighted, free-floating chuck, or an actuator assembly 36 may be attached to the chuck 31 to impart axial and/or rotational motion (indicated by arrows C and D, respectively).
To planarize the wafer 12 with the CMP machine 10, a robotic device (not shown) places the front face 14 of the wafer 12 on a loading/unloading pedestal 50, and the wafer carrier assembly 30 moves the chuck 31 over the backside 15 of the wafer 12. The chuck 31 picks up the wafer 12 and then presses the front face 14 of the wafer 12 against the polishing pad 40. At least one of the platen 20 or the chuck 31 moves relative to the other to planarize the front face 14 of the wafer 12. After the wafer 12 is planarized to a desired endpoint, it is removed from the polishing pad 40, placed on the pedestal 50, disconnected from the chuck 31, and then removed from the pedestal 50 and transported to other processing stations.
One problem with conventional CMP processes is that residual particles from the slurry or the polishing pad remain on the front face of wafers after they have been planarized. The residual particles cause defects on the wafers that adversely affect subsequent semiconductor manufacturing processes and reduce the yield of usable wafers. Thus, to increase the yield, it would be desirable to reduce the number of residual particles on wafers after they have been planarized.
One conventional method for reducing residual particles on planarized wafers is to wash the wafers. Additionally, the wafer carrier and the pedestal are also typically washed between planarizing individual wafers. However, even after washing the wafers, pedestal, and wafer carrier, a significant number of residual particles are often present of the front face of the wafers. Merely washing the wafers and the CMP machine, therefore, is not sufficient to adequately reduce the number of residual particles on the wafers. Thus, it would be desirable to develop an apparatus and method that works with conventional washing equipment to further reduce the number of residual particles on planarized wafers.